Notes. Synthesis, crystal structure and gas-phase photoelectron spectroscopic study of B,B′-bis(1,3-dicyclohexyl-1,3,2-diazaborolidin-2-yl)

Abstract

The highly sterically hindered compound B,B′-bis(1,3-dicyclohexyl-1,3,2-diazaborolidin-2-yl)(1) was prepared by transamination of B₂(NMe₂)₄. It is unreactive towards air or moisture. Crystals of (1) are monoclinic, a= 16.829(3), b= 12.021(2), c= 14.744(3)Å, β= 95.06(2)°, Z= 4, and space group C2/c. The structure was solved by direct methods and refined by full-matrix least-squares calculations to R= 0.097 for 1 247 reflections with I > 3σ(I). The molecule has crystallographic two-fold symmetry and the two halves of the molecule are linked through boron atoms, with B–B 1.721(12)Å. Other ring distances are: mean B–N 1.393(7), mean C–N 1.454(6), and mean C–C 1.494(9)Å. The five-membered ring BN₂C₂ planes form a dihedral angle of 80.7°. Both cyclohexyl rings are in chair conformations. A comparison of the photoelectron spectrum of compound (1) with that of B₂(NMe₂)₄ suggests that both compounds are in a staggered conformation in the gas phase; a reassignment of the B₂(NMe₂)₄ spectrum is proposed.